I have half the valve seals changed in my 305 which i believe to be a 79 or 80 model and it has the little o-ring style valve seals. The engine has been rebuilt and it wasnt but a couple years ago and the valve seals were already leaking. The first 8 seals were very brittle. I am not 100% sure it is the valve seals but i think it is, it smoked on start up and i can see oil all over some of the valve stems looking in the exhaust ports and probably in the intake ports too. If the seals are the problem (i sure hope its not the valve guides, it shouldnt be this thing was rebuilt only a few years ago) then can i install umbrella type seals? Would these be better ? I've already got half of them changed but i didnt oil the seals before i installed them so i think i may take it back apart and oil them so i dont burn them up by running them dry. If i take them out i might as well switch to umbrella types if they are better.

Most SBC's I've done don't have clearance between the valve guide and the spring retainer for umbrella seals. You do know that the o-rings go in the lower groove of the valve stem..correct. Have you checked for guide wear?? Most of the times it is the intake seals that leak since they are under vacuum, the exhaust are under pressure and are less likely to leak to the point you describe. Have you checked to see if the oil drain backs are restricted/plugged?

Ok i think i messed up. I pushed the seals all the way down to the bottom of the valve stem against the guide, instead of putting it in the groove beneath the keepers. The old ones were just floating on the valve stem beneath the groove. So i figured thats where they went.

Ok i think i messed up. I pushed the seals all the way down to the bottom of the valve stem against the guide, instead of putting it in the groove beneath the keepers. The old ones were just floating on the valve stem beneath the groove. So i figured thats where they went.

That may be why you have the problem. I've never seen any get down there when installed correctly, it may have been assembled wrong from the start. You need to compress the spring with the retainer and install the o-ring then the keepers and let the spring come up, the o-ring is actually held within the lower part of the retainer. As I said earlier,most of the heads I worked on as a machinist, had no room between the retainer and top of the valve guide. I imagine it would be tight for the o-ring as well. They may have been pinched as the valves opened and got distorted, so they were useless.

I like the Perfect-Circle style seal. You will take the springs off and then push the seal onto the valve stem and then push it over the valve guide. They are a bit pricey but they last a long time.

Way back when I used the seals from a 195? Studebaker, but I don't think you can buy them anylonger. They fit inside the spring and rode the valve so they would not wear the valve stem where as the PC seal will wear the valve stem over the life time of the engine.

Well ive got them all changed now and unless its using a TON of oil ill probably just leave it alone now. However i did take it all back apart and put the seals in the groove beneath the valve keepers but i didnt notice until i got done that when i compressed the spring to reinstall the keepers that it pushed the seals back down on the stem out of the groove. So im back to where i started i think. Anyways . The end of the dipstick tube is broken off in the block that is the next project to fix. Then finish cleaning and painting and the engine is ready to go in the truck.

I like the Perfect-Circle style seal. You will take the springs off and then push the seal onto the valve stem and then push it over the valve guide. They are a bit pricey but they last a long time.

Scholman

They can't be used without machining the guides to accept them. The guides have to be machined smaller and to insure that they are concentric, which the stock cast ones are not. It also takes some off the top of the guide to give the needed clearance as well as make it perpendicular for a tight fit under the seal. All that requires that the heads be removed, how else can you remove the valves for the machine work? I always use them ( many companies make the same type now, Perfect Circle just introduced them)when I re-do heads, although some thoughts suggest that the stock seal on the exhaust are better because they need a little more lube. So unless he plans on removing the heads, his approach is the only real solution he has...although it sounds as if he may have not retained the seals in their correct position. The philosophy behind having them in the retainers, as I understand it, is to keep the oil dripping off the end of the rocker from running down the stem.

i didnt notice until i got done that when i compressed the spring to reinstall the keepers that it pushed the seals back down on the stem out of the groove.

That's why the spring and retainer need to be compressed WHEN the seal is put on the stem, then when it is released the keeper will come up and keep the seal within it. Hopefully the oil consumption will slow enough to allow you to replenish your energy for a future redo.

I have half the valve seals changed in my 305 which i believe to be a 79 or 80 model and it has the little o-ring style valve seals. The engine has been rebuilt and it wasnt but a couple years ago and the valve seals were already leaking. The first 8 seals were very brittle. I am not 100% sure it is the valve seals but i think it is, it smoked on start up and i can see oil all over some of the valve stems looking in the exhaust ports and probably in the intake ports too. If the seals are the problem (i sure hope its not the valve guides, it shouldnt be this thing was rebuilt only a few years ago) then can i install umbrella type seals? Would these be better ? I've already got half of them changed but i didnt oil the seals before i installed them so i think i may take it back apart and oil them so i dont burn them up by running them dry. If i take them out i might as well switch to umbrella types if they are better.

This is not only an indicator that that the so called seals are gone, but is also a good sign that the guides and possibly the stems are excessively worn.

One reason for fast wear after a rebuild is that either the guides weren't refreshed nor the valves replaced, or if refreshed, the guides were knurled which isn't a long lasting repair and it forms a screw shaped path from the oily side of the guide into the port for oil to travel in. You also have to consider that this process reduces the surface area within the guide, therefore, the unit loading on any square inch of contact surface is higher which nets more and faster wear.

Umbrella seals and the Chevy O ring are not really seals in the sense of the word. They both work to redirect the dripping oil off the valve stem away from the guide not stop its entry, neither can or does actually stop oil from going down the guide once it finds its way onto the stem or upper guide. However, if the guide to stem clearance is in decent shape they will reduce oil consumption by directing oil away from the entry side of the guide.

Positive seals like the Perfect Circle do an excellent job of keeping oil out of the clearance when the guide and stem are in good shape and properly clearanced. Like any-other close fitting seal, if the stem is wandering about in the guide, the seals effectiveness goes out the window pretty fast.

So I guess my recommendation is to check the stem to guide clearance and repair that to spec. as required.

The intake is the hardest to seal oil out as there is aways a running vacuum on the guide, bigger or smaller but when the motor is running that vacuum is there. The exhaust sees pressure against the guide most of the time and is less of a problem, but the running clearance needs to be a bit more so it is easier to get oil into the clearance.

Well i'll be damned. Thanks guys! I didnt know any of this. Sounds to me like these heads were assembled wrong to begin with. I cant feel any side to side movement in the valves inside the guides. Im not sure how you check it otherwise. This part is getting a lil deep for me. Usually heads i leave to the machine shop to do. Now that I have this information tho I may be able to atleast replace the seals sucessfully. If the guides need replaced is that something i can do myself? I know i will need to remove the heads, but that is ok. I didnt PLAN on doing that, but i have a full gasket set so its no problem if i must.

That's why the spring and retainer need to be compressed WHEN the seal is put on the stem, then when it is released the keeper will come up and keep the seal within it. Hopefully the oil consumption will slow enough to allow you to replenish your energy for a future redo.

I didnt know this but thank you for telling me. I just went out and tried it because i have not adjusted the valves yet. However because of the type of spring compressor i have (lever type that you have to bolt down to the rocker stud, it doesnt push the spring down evenly. When i compressed the spring assembly down, and put the seal on the stem, it pushed the seal back up when i released it. Its hard to do all this at once and get the keepers in (and hold the light since i'm outside). I think i need a jaw type compressor to make the job easier.

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